The long-term goal of this project is to identify novel redox base mechanisms that lead to the development of cancer. Our studies have identified the mitochondrial antioxidant enzyme manganese containing superoxide dismutase (MnSOD) as an important regulator that can both modulate the development of cancer and be modulated during the progression of cancer. Our studies in the previous funding period demonstrate that reduction of MnSOD levels occurs very early in the development of skin cancer and that the level of p53 regulates the expression of MnSOD. We also found that the level of the mitochondrial uncoupling protein 1 (UCP1) is significantly increased in skin tissues of MnSOD-deficient mice. We hypothesize that the activities of p53, MnSOD and UCP1 are regulated to minimize reactive oxygen species (ROS) production in mitochondria. We propose that: 1) as a critical transcription factor, p53 cooperates with transcriptional activators and suppressors to regulate MnSOD transcription (Aim 1) and 2) the reduction of MnSOD levels in mitochondria leads to UCP1 induction as a result of compromised mitochondrial function, which induces transcriptional responses to reduce superoxide production from mitochondrial respiration (Aim 2). The positive and negative feedback loops between nuclei and mitochondria help to ensure that superoxide levels are minimized to prevent mitochondrial dysfunction and subsequent neoplastic transformation. We will use state-of-the-art molecular biology, biochemistry and free radical biology approaches to address these specific aims. Because mitochondria are major sites of cellular energy production and cellular ROS homeostasis, and are integrators of apoptosis signaling that are altered in cancer cells, understanding the regulation of mitochondrial ROS levels is important and will provide a unique opportunity to design novel interventions that maximize the benefits to normal tissues and prevent cancer development. Given that cellular redox status contributes to almost all aspects of biological function, and that MnSOD and p53 are critical for normal cellular function and for cancer prevention, the results from this study of cancer will have a broad impact on human health and the prevention of other diseases, including obesity and metabolic disorders.